The present invention relates generally to electric motors, generators, and regenerative motors. The term regenerative motor is used herein to refer to a device that may be operated as either an electric motor or a generator. More specifically, the invention relates to an electric motor, generator, or regenerative motor including a stator arrangement which itself includes a plurality of individual electromagnetic assemblies with each independent electromagnetic assembly including an associated one-piece magnetic core formed from thin film soft magnetic material.
The electric motor and generator industry is continuously searching for ways to provide motors and generators with increased efficiency and power density. For some time now, it has been believed that motors and generators constructed using permanent super magnet rotors (for example cobalt rare earth magnets and Neodymium-Iron-Boron magnets) and stators including electromagnets with magnetic cores formed from thin film soft magnetic material have the potential to provide substantially higher efficiencies and power densities compared to conventional motors and generators. Also, because cores formed from thin film soft magnetic material are able to respond to changes in a magnetic field much more quickly than conventional ferrous core materials, magnetic cores formed from thin film soft magnetic material have the potential to allow much faster field switching within motors and generators, and therefore allow much higher speed and better controlled motors and generators than conventional ferrous cores. However, to date it has proved very difficult to provide an easily manufacturable motor or generator that includes magnetic cores formed from thin film soft magnetic materials. Furthermore, the configurations that have been disclosed to date do not take full advantage of the capabilities of these potentially more efficient materials for certain types of applications.
Thin film soft magnetic materials such as amorphous metal are typically supplied in a thin continuous ribbon having a uniform ribbon width. In the past, amorphous metal cores have been formed by rolling an amorphous metal ribbon into a coil, annealing the winding, and then saturating and encapsulating the winding using an adhesive such as an epoxy. However, this material is a very hard material making it very difficult to cut or form easily, especially once it has been laminated into a bulk piece. Also, once annealed to achieve peak magnetic properties, these materials become very brittle. This makes it difficult and expensive to use the conventional approach to constructing a magnetic core.
Another problem with amorphous metal magnetic cores is that the magnetic permeability of amorphous metal material is reduced when it is subjected to physical stresses. This reduced permeability may be considerable depending upon the intensity of the stresses on the amorphous metal material. As an amorphous metal magnetic core is subjected to stresses, the efficiency at which the core directs or focuses magnetic flux is reduced resulting in higher magnetic losses, reduced efficiency, increased heat production, and reduced power. This phenomenon is referred to as magnetostriction and may be caused by stresses resulting from magnetic forces during the operation of the motor or generator, mechanical stresses resulting from mechanical clamping or otherwise fixing the magnetic core in place, or internal stresses caused by the thermal expansion and/or expansion due to magnetic saturation of the amorphous metal material.
In U.S. Pat. Nos. 5,982,070 and 6,259,233 that issued to the applicant and that are both incorporated herein by reference, certain methods and arrangements for constructing electric motors and generators were described. In these patents, hereinafter referred to as the ""070 patent and ""233 patent respectively, multiple amorphous metal core pieces are supported in a dielectric housing to form an overall amorphous metal core. Another U.S. Pat. No. 4,255,684 issued to Mischler et al. describes another motor configuration that utilizes amorphous metal materials. Although these approaches allow motors and generators to be constructed using amorphous metal cores, there are some inherent problems associated with these approaches. For example, the use of multiple core pieces to form the overall core means that there are parasitic gaps between adjacent core pieces that the magnetic flux has to cross as the flux flows through the magnetic core. These parasitic gaps occur at any point that the flux must pass from one piece or layer of core material to another. Although these gaps may be made very small by manufacturing the various core pieces to very tight tolerances, and may be filled with epoxy, they still result in parasitic losses that reduce the efficiency at which the flux can flow through the core compared to a core that does not have these gaps.
In addition to the parasitic gap problem, the methods and arrangements of the ""070 and ""233 patents make it difficult to always orient the amorphous metal magnetic material in the proper orientation. This is especially true of the radial gap devices disclosed in these patents. The proper orientation of the thin film soft magnetic material is important to maximizing the efficiency at which the magnetic flux is able to flow through the core material, and therefore, the efficiency of the device.
In the case of the axial gap configurations disclosed in the ""070 and ""233 patents, the physical configuration of the axial gap device makes it difficult to maintain the proper air gap between the rotor and the stator. Because the magnetic forces act axially along the rotational axis of the device, expensive bearings having very tight tolerances must be used to support and hold the rotor in place. Also, the housing materials supporting the stator must be able to withstand these very high axial forces without deforming over the life of the device. Furthermore, since the stator and rotor supporting members are members that are substantially disk shaped and are generally planar, they are more susceptible to warping or deformation due to the large axial magnetic forces and due to internal stresses caused by temperature changes that occur regularly during normal operation of the device. As larger and larger axial gap devices are contemplated, the magnetic forces between the rotor and stator become larger and larger further compounding this problem.
The present invention provides improved methods and arrangements for providing electric motors, generators, and regenerative motors that use magnetic cores formed from thin film soft magnetic core materials. The present invention also provides for improved electric motor, generator, and regenerative motor configurations that more fully utilize the potential benefits associated with using magnetic cores formed from thin film soft magnetic materials.
As will be described in more detail hereinafter, magnetic cores for use as part of a stator arrangement in a device such as an electric motor, an electric generator, or a regenerative electric motor are disclosed herein. Stator arrangements and methods of making stator arrangements utilizing the magnetic cores, and devices and methods of making devices utilizing the stator arrangements, are also disclosed. The device includes at least one stator arrangement having a plurality of electromagnetic assemblies with each electromagnetic assembly including at least a portion of a magnetic core that is formed from thin film soft magnetic material. The electromagnetic assemblies define a plurality of stator poles. The device also includes at least one rotor arrangement supported for rotation about a given rotational axis at a certain range of normal operating rotational speeds. The rotor arrangement has a plurality of rotor poles for magnetically interacting with the stator poles. The rotor poles are supported for rotation about the rotational axis along a circular path. A switching arrangement for controlling the electromagnetic assemblies is configured such that the switching arrangement is able to cause the stator poles of the electromagnetic assemblies to magnetically interact with the rotor poles of the rotor arrangement within a certain range of frequencies. The number of rotor poles is selected to be a number such that the switching arrangement causes the stator poles of the electromagnetic assemblies to magnetically interact with the rotor poles of the rotor arrangement in a way which causes the ratio of the frequency of the device in cycles per second relative to the revolutions per minute of the device to be greater than 1 to 4 during the operation of the device.
In one embodiment, the rotor arrangement includes at least 30 rotor poles and the stator arrangement includes at least 48 stator poles. In this embodiment, the device is a radial gap device and the thin film soft magnetic material is a nano-crystalline material. The device may be a device selected from the group of devices consisting of a switched reluctance device, an induction device, or a permanent magnet device. The device may also be either a single-phase device or a multiple-phase device.
In another embodiment, the device is a radial gap device and the electromagnetic assemblies include independent U-shaped one-piece magnetic cores. Each electromagnetic assembly defines two stator poles located at opposite ends of the one-piece magnetic core. Each one-piece magnetic core provides the entire magnetic return path for the two opposite magnetic stator poles associated with each electromagnetic assembly. The electromagnetic assemblies are positioned around the circular path of the rotor poles and each electromagnetic assembly is positioned such that the two stator poles of each electromagnetic assembly are located adjacent to one another and in line with one another along a line that is parallel with the rotational axis of the device. In one version of this embodiment, the rotor poles are pairs of rotor poles formed from adjacent pairs of permanent magnet segments configured to form rotor poles of opposite magnetic polarity. Each pair of permanent magnet segments is positioned such that the two permanent magnet segments are located adjacent to one another and in line with one another along a line that is parallel with the rotational axis of the device. The two permanent magnet segments define two adjacent circular paths around the rotational axis of the device when the rotor is rotated about the rotational axis of the device with each of the two adjacent circular paths facing an associated one of the stator poles of each electromagnetic assembly. In this version, the rotor arrangement includes at least 36 pairs of adjacent rotor poles and the stator arrangement includes at least 48 electromagnetic assemblies. The stator poles may face inward toward the rotational axis of the device, or, alternatively, the stator poles may face outward away from the rotational axis of the device.